Adolescence is a critical period for the acquisition and configuration of healthy dietary habits and lifestyle for the young future, which will likely persist throughout the adulthood. Paediatric and juvenile obesity is a public health problem which control necessarily implies prevention and nutritional education.To evaluate the nutritional status of the adolescents and determine the proportion with overweight or obesity, and to establish a Nutritional Intervention Programme and analyse the improvement in the pattern of dietary habits among the adolescents.The study has been carried out in a population of 372 Obligatory Secondary Education (OSE) students from the Institute of Secondary Education of Gandía (Valencia).37.8% of the adolescents have improved the level of their diet quality. Those consuming a high quality diet have increased from 30.0% to 58.6%. Also significant is the number of students that have taken up having breakfast and those having discontinued taking industrial bakery with this meal. The decrease in the number of adolescents going to fast food places and of those that have discontinued eating candies regularly is statistically significant. The data from the KIDMED index show that 47.4% (p < 0.001) of de the students have improved the quality of their diet and in none of them it has worsened.Before starting the programme, 30% of the students followed a high quality diet comparable to the traditional Mediterranean Diet, and after the education programme, this percentage increased to 58.6%. Forty-seven point four percent of overweighed or obese students receiving the Nutritional Education and Intervention have improved their diet quality and the percentage of those following a high quality diet varied from 28.9% to 71.0%.